Clutch Recommendation?

[James B.]

I am at the point in restoring my 67 L79 coupe that I need to order a clutch so that when my engine builder can balance the clutch to flywheel. The engine will be close to original specs (true 10.3 CR, flat tappet cam, heads ported a bit, not overbored, not decked, etc) so it will be close the original "350" gross HP (or whatever an L79 truly was!!). I want a clutch that has fairly light pedal pressure but grabs well when needed.
The only recommendation I have gotten is for a Centerforce dual friction clutch. I have driven a 66 small block with that clutch and liked it's feel and grip. Does anyone have anything different to suggest?
I went back in the archives but the newest discussion I found was 2011 & I'm reluctant to go with 4 year old info.
Thanks in advance, JimB

[Joe L.]

Re: Clutch Recommendation?

I am at the point in restoring my 67 L79 coupe that I need to order a clutch so that when my engine builder can balance the clutch to flywheel. The engine will be close to original specs (true 10.3 CR, flat tappet cam, heads ported a bit, not overbored, not decked, etc) so it will be close the original "350" gross HP (or whatever an L79 truly was!!). I want a clutch that has fairly light pedal pressure but grabs well when needed.
The only recommendation I have gotten is for a Centerforce dual friction clutch. I have driven a 66 small block with that clutch and liked it's feel and grip. Does anyone have anything different to suggest?
I went back in the archives but the newest discussion I found was 2011 & I'm reluctant to go with 4 year old info.
Thanks in advance, JimB

Jim------


If you liked the Centerforce Dual Friction clutch, then I'd go with it. It will be exactly the same for your 67 as it was for the 66 small block you drove. Personally, it's not a clutch I would use but, it's a good clutch and, if you like it, I'd say that's the way to go.

If it were me, I'd use a LUK clutch. That will be the closest to the original stock clutch.

[Jim D.]

Re: Clutch Recommendation?

Jim------



If it were me, I'd use a LUK clutch. That will be the closest to the original stock clutch.

I've had good luck with Luk clutches BUT be sure to have everything balanced. With the last Luk set-up I bought, the pressure plate was SEVERELY out of balance.

[Joe L.]

Re: Clutch Recommendation?

I've had good luck with Luk clutches BUT be sure to have everything balanced. With the last Luk set-up I bought, the pressure plate was SEVERELY out of balance.

Jim------


Yes, ANY clutch assembly should be balanced prior to installation. This was even true of GM clutches. I've seen several that were WAY off.

[Jim D.]

Re: Clutch Recommendation?

Jim------


Yes, ANY clutch assembly should be balanced prior to installation.

I agree 100% but I posted the same reply on a different car forum and you should have seen the replies. Everything from " I have no idea what I'm talking about" to " You're just wasting customers money". I guess there is no cure for STUPID.

[Leif A.]

Re: Clutch Recommendation?

OK, I'll bite. I was always taught that the only dumb question was the one not asked. How does one go about balancing a clutch assembly? Installed quite a few years ago and never balanced one. Curious for future installations.

[Joe L.]

Re: Clutch Recommendation?

OK, I'll bite. I was always taught that the only dumb question was the one not asked. How does one go about balancing a clutch assembly? Installed quite a few years ago and never balanced one. Curious for future installations.

Leif------

Balancing has to be done by a balancing shop with specialized equipment; it's not something you can do yourself. The flywheel, pressure plate and friction disc should be all done at the same time.

Sometimes, you can install a clutch without balancing and you get lucky as is, apparently, what happened to you. Other times, after a new clutch is installed one gets driveline-induced vibration, sometimes severe and ALWAYS annoying. Then, one gets to "go back in", remove the clutch, and do what one should have done in the first place----have it balanced.

Would I ever install a clutch without first having it balanced? NEVER. EVER.

[Duke W.]

Re: Clutch Recommendation?

The common and inexpensive Luk, Sachs, or Borg Warner clutch should work fine as long as you don't plan on doing a lot of 5000 rev clutch drops. It's good for normal road use. I believe that are all the same - just different distribution channels for each "brand".

Original GM flywheels and clutch covers were balanced separately and stamped with an "X". Upon installation the two X marks are to be aligned as close as possible to yield the least imbalance of the assembly.

In the field the flywheel should be balanced first, and any unbalance is usually adjusted by drilling the flywheel. Then the cover should be bolted on and the assembly balanced by adding or subtracting welded on weights to the cover.

Then the flywheel and clutch cover assembly orientation should be clearly marked.

Duke

[Leif A.]

Re: Clutch Recommendation?

Thank you, Joe and Duke. Great information for me going forward.

[Paul D.]

Re: Clutch Recommendation?

OK, keeping in mind Leif's comment about dumb questions... Can a flywheel for a externally balanced engine such as the 400 SBC or 454 BBC be balanced independently from the rotating assembly? Chip.

[Joe L.]

Re: Clutch Recommendation?

Original GM flywheels and clutch covers were balanced separately and stamped with an "X". Upon installation the two X marks are to be aligned as close as possible to yield the least imbalance of the assembly.


Duke

Duke-----


Just to be clear so that everyone understands, this applies to PRODUCTION flywheels and clutch covers. In SERVICE, flywheels and clutch covers were never available as a unit and no balance marks were found on either flywheels or clutch covers. Supposedly, they were each neutral-balanced but clutch covers, in particular, were often "off".

[Joe L.]

Re: Clutch Recommendation?

OK, keeping in mind Leif's comment about dumb questions... Can a flywheel for a externally balanced engine such as the 400 SBC or 454 BBC be balanced independently from the rotating assembly? Chip.

Paul------


Yes.

[Duke W.]

Re: Clutch Recommendation?

OK, keeping in mind Leif's comment about dumb questions... Can a flywheel for a externally balanced engine such as the 400 SBC or 454 BBC be balanced independently from the rotating assembly? Chip.

The short answer to your question is no, and here's why:

Cruciform crankshaft V8s can be statically balanced by adding appropriate balance mass opposite each crank throw to balance rotating mass. However this leaves a residual dynamic unbalance - a rocking couple due to reciprocating mass - the pistons and top of the rods.

To balance this couple some of the mass used to balance the rotating forces is shifted from the center of the crank to the ends. This maintains static balance while balancing the rocking couple. This is why you typically see no counterweights on the center journals, but very large counterweights at the ends of the crank.

Tire balancing is the same. Static balance can be achieved by placing weights on just one side or splitting in any proportion between the inside and outside. However, the assembly may not be dynamically balanced due to a rocking couple and any significant dynamic unbalance may cause the assembly to wobble slightly, which you can often feel as "steering wheel wiggle". Most tire shops, nowadays, have dynamic balancers, and that's why there are weights on both sides of unequal value and not aligned along the same radial line. The total balance mass balances the assembly statically, and the radial distribution of usually unequal weight between the inside and outside balances the assembly dynamically.

Most Chevrolet engines are balanced "internally" - all the balance mass is on the crankshaft. However the 400 SB and 454 are examples of "externally balanced" engines. Some of the balance mass is on the flywheel and torsion damper. On these engines the flywheel and damper must be bolted to the crankshaft and balanced as an assembly, then installed on the engine indexed the same way they were when balanced.

The clutch cover should then be neutral balanced, and specific orientation to the flywheel is not required.

I'm not sure if all shops have proper equipment to balance the damper-cranshaft-flywheel assembly, so if you have an externally balanced engine configuration you need to verify that the shop has equipment that can balance the entire flywheel-crank-damper assembly.

Duke

[James B.]

Re: Clutch Recommendation?

Joe, you said, "Personally, it's not a clutch I would use but, it's a good clutch". Interesting reply, can you please say more re why you would not use the Centerforce. The only negative I read in the archives was one person saying the weights clattered at idle (my car will be judged so I am a little concerned about that). My restorer/advisor questions Luk. He has used several over the years and had trouble with a couple. Maybe as Jim Durham says in the next post he believed Luk that they were balanced at the factory & they were off??

[Joe L.]

Re: Clutch Recommendation?

The short answer to your question is no, and here's why:

Cruciform crankshaft V8s can be statically balanced by adding appropriate balance mass opposite each crank throw to balance rotating mass. However this leaves a residual dynamic unbalance - a rocking couple due to reciprocating mass - the pistons and top of the rods.

To balance this couple some of the mass used to balance the rotating forces is shifted from the center of the crank to the ends. This maintains static balance while balancing the rocking couple. This is why you typically see no counterweights on the center journals, but very large counterweights at the ends of the crank.

Tire balancing is the same. Static balance can be achieved by placing weights on just one side or splitting in any proportion between the inside and outside. However, the assembly may not be dynamically balanced due to a rocking couple and any significant dynamic unbalance may cause the assembly to wobble slightly, which you can often feel as "steering wheel wiggle". Most tire shops, nowadays, have dynamic balancers, and that's why there are weights on both sides of unequal value and not aligned along the same radial line. The total balance mass balances the assembly statically, and the radial distribution of usually unequal weight between the inside and outside balances the assembly dynamically.

Most Chevrolet engines are balanced "internally" - all the balance mass is on the crankshaft. However the 400 SB and 454 are examples of "externally balanced" engines. Some of the balance mass is on the flywheel and torsion damper. On these engines the flywheel and damper must be bolted to the crankshaft and balanced as an assembly, then installed on the engine indexed the same way they were when balanced.

The clutch cover should then be neutral balanced, and specific orientation to the flywheel is not required.

I'm not sure if all shops have proper equipment to balance the damper-cranshaft-flywheel assembly, so if you have an externally balanced engine configuration you need to verify that the shop has equipment that can balance the entire flywheel-crank-damper assembly.

Duke

Duke------

SERVICE 400 cid and 454 cid flywheels are intended to be used "out-of-the-box". They have "no idea" what crankshaft they are going to be bolted to or what balancer is going to be installed on that crankshaft. Whatever means the factory uses to balance these SERVICE flywheels can be duplicated and even improved on at a custom balancing shop.